In astronomy news this week, astronomers announce the most distant solar system object discovered to date and estimate the limited lifetime of Saturn's spectacular rings.

Most Distant Solar System Object Discovered

Nicknamed "Farout," the object provisionally known as 2018 VG18 currently orbits the Sun somewhere between 115 and 125 astronomical units (a.u.), roughly 3½ times farther out than Pluto. This find beats the distance record previously set by Eris, which is currently at 96 a.u.

Farout art
Artist concept of 2018 VG18 "Farout," with a scale of Solar System distances plotted at the bottom.
Roberto Molar Candanosa / Carnegie Institution for Science

Scott Sheppard (Carnegie), David Tholen (University of Hawaii), and Chad Trujillo (Northern Arizona University) discovered the object in November using the 8-meter Subaru telescope on Mauna Kea, Hawai'i. Graduate student Will Oldroyd (Northern Arizona University) joined the team for further observations in early December from the Magellan telescope at the Las Campanas Observatory in Chile. The additional images helped the scientists determine the object's distance, as they measured its motion against far more distant background stars. The Minor Planet Center announced Farout's discovery on Monday.

The team found Farout as part of their search for Planet X, a super-Earth-size world that might be shaping the orbits of several distant solar system objects. However, depending on the shape of the Farout's orbit, it will take another year or three before the team can nail down its orbital parameters and determine whether it, too, has been influenced by the putative Planet X.

Will Saturn's Rings Disappear?

Many an amateur begins their night — and perhaps even their observing career — with a view of Saturn's magnificent rings. But a new study shows this solar system spectacle might be short-lived.

When Cassini's final orbits took it inside the rings' inner edge, its last observations returned some surprising data. While the rings have been known to be precipitating down onto the planet since Voyager 2's pass by the planet in 1981, Cassini data showed that this gravitationally driven "ring rain" had been vastly underestimated. Now, James O'Donaghue (NASA Goddard) and colleagues have conducted a new analysis of ground-based data from 2011, taken at the Keck telescope on Mauna Kea, Hawai'i, revealing that, in addition to raining down on the equator via gravity, icy ring particles also flow in along magnetic field lines to reshape the chemistry of the planet's outer atmosphere. Combined with Cassini data, the new analysis enables the researchers to estimate the rings' remaining lifetime: less than 100 million years, a mere blink in Saturn's 4 billion-year lifetime. The results appear in Icarus.

"None of the other gas giants have rings anywhere near the mass and brightness of that seen at Saturn," says coauthor Tom Stallard (University of Leicester, UK). "It strongly suggests that something significant must have happened in the recent geological history of Saturn’s system, and that going back to the age of the dinosaurs, Saturn’s rings must have been even more impressive."

Interestingly, simulations of the dynamics in the Saturnian system, conducted a couple years ago by Matija Ćuk (SETI Institute) and colleagues, suggest that Saturn's mid-size moons are also about 100 million years old. "The idea that not only the rings but also many of Saturn’s moons are new is a daunting one, unsettling even," Stallard says, "but it certainly chimes with the surprisingly young age that our observations suggest for the rings."


Image of Anthony Barreiro

Anthony Barreiro

December 21, 2018 at 7:17 pm

I'm grateful to live in a moment when I can see Saturn's rings through my little telescope.

Jupiter, Uranus, and Neptune all have very faint rings. Is there reason to believe that these planets' rings were bigger and brighter in the past? If so, any inferences on when they would have been at their best? I'm imagining Jupiter at a solstice opposition surrounded by huge rings with a blindingly bright Seeliger effect!

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